The present invention relates to a numerical control information generating apparatus for preparing information used to numerically control a numerical control machine tool according to data denoting the shapes of a starting material and a finished part, and a method for determining a machining mode thereof.
In a numerical control machine tool, numerical control information must be input prior to machining. Hence, an apparatus capable of easily preparing and generating numerical control information is used. With such a numerical control information generating apparatus, machining data consisting of the quality and shape of a material and machining modes (areas to be machined, cutting direction, cutting tool, sequence of machining, etc.) are input by an operator on an interactive basis to enable numerical control information to be obtained. In recent years, a numerical control information generating apparatus has been used which automatically determines the machining modes according to only the input data denoting the shapes of a starting material and a finished part and prepares numerical control information.
A method for determining the machining modes, for example, for a recessed shape as shown in FIG. 2 using such a numerical control information generating apparatus will be explained with reference to the flow chart of FIG. 1. First, data denoting the shapes of the starting material and finished part are input and a machining area R.sub.0 is determined by comparing the two shapes (Step S1). Since this machining area R.sub.o is located at an outer circumference, the cutting direction is initially determined to be in a forward longitudinal direction (.rarw.) (Step S2). It is then determined whether or not a downward cut is needed by comparing a figure element list l.sub.3, l.sub.4, l.sub.5 constituting the shape of the machining area R.sub.0 and the cutting direction (forward longitudinal (.rarw.)). When a downward cut is not needed, it is determined that the figure element list does not constitute a recessed shape (Step S3). A tool is selected according to the cutting direction (Step S9) and the operation proceeds to Step S10.
In the case of FIG. 2, however, a downward cut is needed since the figure element l.sub.3 exists, and the figure element list l.sub.3, l.sub.4, l.sub.5 is thus determined to be a recessed shape (Step S3). A forward longitudinal machining tool (FIG. 5A), which is the first tool, is selected by the result of this determination (recessed shape) and the cutting direction (forward longitudinal (.rarw.)) (Step S4). By comparing an angle .alpha. formed by the recessed downward shape (figure element l.sub.3) relative to the Z-axis and an angle .beta. (hereinafter referred to as "sub cutting blade angle") formed by the sub cutting blade of a forward longitudinal machining tool relative to the Z-axis, it is determined whether or not the blade of the forward longitudinal machining tool will be interfered with during downward cutting (Step S5). In the case of .alpha.&lt;.beta., no interference occurs and a downward cut can be performed, and therefore the operation proceeds to the Step S10. In the case of FIG. 2, however, .alpha..gtoreq..beta. and an interference occurs. Therefore, as shown in FIG. 3, a figure element l.sub.s which intersects the start point A of the downward element l.sub.3, and which makes an angle with respect to the Z-axis, which is greater than the sub current blade angle .beta., is created. The figure element l.sub.4 is divided into a figure element l.sub.4 ' and a figure element l.sub.4 " at an intersecting point B of the figure element l.sub.4 and the figure element l.sub.s. The machining area R.sub.0 is divided into machining areas R.sub.1 and R.sub.2 (Step S6). The cutting direction of the machining area R.sub.2 is determined to be in a reverse longitudinal direction (.fwdarw.) (Step S7). A reverse longitudinal machining tool (FIG. 5B), which is the second tool, is selected according to this cutting direction (reverse longitudinal (.fwdarw.)) (Step S8). Cutting conditions and machining sequences are determined (Steps S10 and S11). Numerical control information is prepared on the basis of the machining modes determined as mentioned above, and all processes are terminated. Finally, a tool trace, as shown in FIG. 4, is obtained according to this numerical control information.
For example, in a case where the starting material and the finished part both contain recessed shapes, as shown in FIG. 6, the tool trace which is obtained from the numerical control information prepared by inputting these shape data into above-mentioned conventional numerical control information generating apparatus as shown in FIG. 7. In this tool trace, there has been a problem in that an idle cutting is performed in a portion within a recess of a material where cutting is not required and therefore the overall cutting time is increased.